During recent years the cement industry has suffered significant increases in operating costs driven in particular by spiralling energy prices plus pressure from environmental lobbies to reduce dependence on fossil fuels and reduce CO2 emissions overall. Considering that the production of a ton of conventional Portland cement generates almost a ton of CO2, and in terms of total greenhouse gas emissions for all industries worldwide, this places cement second only to the power industry in the scale of global polluters.

These factors have generated an increased awareness of alternative fuel possibilities for kiln firing and substitute raw material options for cement production, also reflecting an increased demand for blended cements particularly including ground granulated blast furnace slag (GGBFS). This last point is particularly important; for every ton of GGBFS included in the final blended cement the total CO2 production is reduced by around 1t.

Air-cooled slags can exhibit a peculiar volume instability upon cooling and disintegrate into a fine powder. The outcomes of this are severe dust issues in the surroundings of the meltshop and forced landfilling, since a powdery slag cannot be applied as an aggregate for construction applications. In this article, the causes of this disintegration is discussed, in addition to an evaluation of the dusting behaviour of a particular slag based on the overall slag composition, and how borates can be used to stabilise the slags.

Certain types of slag disintegrate on cooling, (see Figure 1. It is well known that this particular kind of volume instability is caused by the presence of dicalcium silicate, 2CaO•SiO2, (C2S) in the slag structure. This mineral undergoes several phase transformations during the cooling of hot slag. The last transformation from the β to the γ polymorph at approximately 400°C is accompanied by a 12% volume expansion, which causes high internal stresses in the slag and, subsequently, the disintegration into a fine powder. The resulting particle sizes are typically not larger than 100µm.

Over time, this volume instability has been observed with various slag types, ranging from blast furnace slags to steelmaking slags. At present, however, the problematic disintegration is primarily encountered in two areas. Firstly, in stainless steelmaking, decarburisation slags are known to heavily disintegrate during cooling. EAF slags also display this behaviour, but to a lesser extent. Secondly, aluminium-killed ladle refining slags in steelmaking may disintegrate as well.

The UK in recent years has experienced substantial price increases and supply rationing in both the Portland cement and slag cement industries. Cenin Ltd has developed a centre of excellence to produce cement substitutes equivalent to slag cement using 100% renewable energy and 100% recycled materials, probably the first of its type in the world today. The company's carbon footprint is probably one of the smallest footprints in cement-related industries. As a result, Cenin Ltd is in a position to partially fill this gap with an alternative cement substitute.

For the first time in our knowledge, the UK construction industry has been experiencing rationing of Portland cement and slag cement. This is also found to be the case in many US states. This situation has highlighted that there is an opportunity for alternative cement substitutes within the construction industry, both in the UK and the US.

In the UK and many other countries, landfill sites in general are becoming over-crowded and expensive for waste producers. As a result, and wherever possible, material going to disposal should therefore be minimised. If the production of the waste cannot be prevented, then it is attractive to create an alternative use in another process before considering disposal.

Ecocem Ireland Ltd. is leading the way in championing the use of GGBFS in cement manufacture. In this paper, Peter Seymour of Ecocem Ireland discusses Ecocem's business strategy that includes industry-leading research and design, extensive brand promotion and dialogue with EU countries to help change national norms and specifications. A selection of business case studies from the Benelux and UK cement markets are also described. Also featured is an analysis of environmental advantages of Ecocem's pioneering Carbon Neutral Concrete.

Ecocem Ireland and Orcem BV manufacture and sell ground granulated blast furnace slag (GGBFS) in the Irish and Benelux markets respectively. Both companies are wholly-owned subsidiaries of Ecocem Materials Ltd., an Irish company set up in 2001 to undertake industrial developments in Europe in the production and use of GGBFS.

Ecocem Ireland (Ecocem) operates a closed circuit drying and grinding ball-mill for the manufacture of GGBFS. The plant is located in the port of Dublin, and Ecocem has been manufacturing GGBFS at this location since late 2003.

Orcem BV (Orcem) operates a similar closed circuit drying and grinding roller-mill. The Orcem plant is located in Moerdijk, near Rotterdam. Orcem has been manufacturing GGBFS at Moredijk since 2001.

At Voestalpine Stahl, 646,000t of LD slag is produced annually, most of which is used in bituminous road construction, where two main quality parameters (free lime content and steam testing) have to be met. In this paper the swelling of the slag and the influences on stability (correlation between lime saturation and free lime content) are described. Possible ways of detecting the slag composition are also detailed. Only an in situ measurement of each slag pot can deliver results for each slag tapped. For this purpose a LIBS (Laser Induced Breakdown Spectroscopy) system seems to be most suitable.

The annual amount of LD-slag produced at Voestalpine Stahl (Linz) is 646,000t. Approximately 75% of this slag is used in bituminous road construction, about 12% for recycled iron, while the rest is used internally and in the cement industry. Figure 1 below shows the utilisation of Voestalpine LD slag. For this application, the slag must meet two quality criteria: